where \(n_{\mathfrak {g}}\)  is 2 for \(F_4\) , 3 for \(G_2\) , and 1 for other semisimple classical groups [1]}; \(\tau \)  is usual gauge coupling constant and \(G^{L}\)  is Langlands dual group of \(G\) .
In [2]}, Gukov and Witten extended their earlier analysis and identified a subclass of surface operators called 'rigid' surface operators expected to be closed under \(S\) -duality.
There are two types rigid surface operators: unipotent and semisimple. The rigid semisimple surface operators are labelled by pairs of partitions \((\lambda ^{^{\prime }}, \lambda ^{^{\prime \prime }})\) . Unipotent rigid surface operators arise when one of the partitions is empty.
